That's simple. When you pass arguments by value (no pointer, no reference), they're copied and all operations are performed on said copies.

try

Code:

float exchange (float &a, float &b)
{
    float aux;
    aux=a;
    a=b;
    b=aux;
}

exchange (x[i], x[j])

 

Krazq is correct that variable scope is your issue, but his answer doesn't quite work either.

 

I beg to differ

While we're on this topic, how can you explain this?

 

Sorry if I wasn't clear. Obviously C allows you great latitude with abusing variable type and your answer *works*, but since you didn't use explicit typecasting if I was the TA and you turned that in I would assume that you didn't understand the difference between float, &float, and *float and would grade you accordingly.

 

Nukular... why the hell would you mark that down? If you /do/ use explicit typecasting, I understand marking someone down, but a float and a float reference (&float) are exactly the same type, and should be used that way.

 

In an intro to programming class?

 

Typically it's taught that variables are passed either by value (a copy is made) or by reference (treat it as the actual value). Adding a by-reference flag lets you use it as if it wasn't part of the function at all.

float and &float are not different types, and should never be treated that way, especially in an intro class.

Then again, I don't believe C should be an intro class, but most languages have a byref and byval declaration.

 

I don't quite understand why would you makt it down. Do you consider using explicit typecasting whenever possible a good coding habit?

 

I just looked it up to see if I was smoking crack, and apparently that's actually how you pass by reference in that newfangled C++. (I learned C and pretty much used it for everything). Humbug.

In good old C, passing by reference would look something like this:

Code:

#include <stdio.h>

void swap(int *i, int *j) {
   int temp = *i;
   *i = *j;
   *j = temp;
}

void main() {
   int a = 42, b = 69;
   printf("Before. a: %d, b: %d\n", a, b);
   swap(&a, &b);
   printf("After . a: %d, b: %d\n", a, b);
}

At any rate, Mea Culpa and full points to you.

/Get off my lawn

 

Which is what I ended up doing. Well, at least I solved most of the question I had for the exam tomorow, now I'm off to go shoot some zombies on LFD2. Thanks for the help guys.

Edit to keep the topic alive: What kind of language most of you use to program nowadays? I've been drifting a bit along my C class this semester, and probably will need to learn some assembly for a couple projects I'm helping out.

 

I use Java a lot at my job. I use perl a lot more than I would like to as well. :-|

 

I mostly write in C and C++ and am most competent in C. I cut my teeth in programming writing Vax-11 assembly.

 

I first learned Python, then some C, then Java. I mostly use Java and Python nowadays, although I'm trying to work my way through SICP at the moment and in the process am learning Scheme.

 

Learned Java for 2 years, though I'm afraid I don't remember much anymore...

 

I started with Ruby, was taught Pascal, and am studying HTML and XML, Visual Basic, Java, and am hoping to study C++.

 

Hmmm lemme see, this semester ACL2 (a subset of Common Lisp), Java, C++, C#, Objective-C, and a little bit of Python and Matlab when the occasion called for it (technically Dalvik as well but thats basically Java). God this semester sucked balls.

 

I wouldn't call HTML/XML a programming language.

Anyway, I'm pretty good with C/C++ and I've written a fair share of helloworlds in Ruby, PHP and x86 assembly (Intel syntax). I also coded a little in Java and MatLab's scripting language.

Should I mention RegExp as well?